With electron microscopy techniques the major virus pathogens of artificially infected Penaeus chinensis were studied. It showed that there are two kinds of virus pathogens in diseased shrimps: spherical virus and baculovirus. Sometimes they were co - existing in the same tissue or even in the same cell. It suggested that a mixed infection maybe occurred. Using immunogold labelling method to label the spherical viruses appearing in the cytoplasm of diseased shrimp, preliminary results showed that the purified spherical viruses were the same as those observed in the infected cells. During the infection, prominent changes took place in main cell organelles of the host cell, such as mitochondrias, endoplasmic reticulum, and ribosome. Especially in late infection, a lot of lysosomes and various multilayered membrane structures were found, some nuclei were wrapped up by some microtubule structures.